1. Field of the Invention
The present invention relates to a microwave power amplification apparatus and method thereof by using, particularly, period-one nonlinear dynamics of semiconductor lasers.
2. Description of the Related Art
Communication networks are generally classified into wireless networks and wireline networks. In the wireless networks, microwaves are used as carriers to deliver data through air to provide communication between mobile electronic devices. In the wireline networks based on optical technologies, optical waves function as carriers to deliver data through optical fibers to provide communication between immobilized electronic devices. These two networks depend on completely different communication approaches and cover completely different communication scopes. Due to the rapid advances of broadband wireless technologies and also due to the various developments of online applications, the capacity demand for data transmission in the wireless networks increases considerably. If the wireless networks are required to manage both the front-end data transmission between users and wireless base stations and the back-end data transmission between the wireless base stations and central offices, currently developed broadband wireless technologies are not capable of meeting the vast capacity demand for data transmission when the wireless networks are simultaneously accessed by a variety of different users or devices.
Since each channel of the wireline networks based on optical technologies provides data transmission capacity of the order of a few Gbits/s to tens of Gbits/s, the optical communication networks are highly suitable to work as backbones for huge back-end data transmission for various network applications. Therefore, radio-over-fiber (RoF) networks which integrate the wireless networks (responsible for the front-end data transmission) and the optical wireline networks (responsible for the back-end data transmission) have become very attractive for the next generation of communication technology and system.
To ensure the communication quality in the RoF networks, the power of the microwaves needs to be high enough. Three approaches are commonly adopted to increase the microwave power. In the first approach, electronic microwave amplifiers are used after photo-detection at base stations. However, to fulfill the demand of considerably increasing data transmission in the future, significantly more data bandwidth is necessary. This therefore requires continuous upgrade or replacement of the electronic microwave amplifiers with higher bandwidth capability, suggesting an enhancement of operation cost. In the second approach, optical power amplifiers are used before photo-detection to increase the power of the input optical signals upon photodetectors. However, too much of the input optical power would damage the photodetectors. In the third approach, the optical modulation depth of the input optical signals is increased, which in turn increases the microwave power after photo-detection under the same received optical power. This can be achieved by increasing the microwave power when directly or externally modulating semiconductor lasers. However, nonlinear effects, such as harmonic or intermodulation distortion, are generally induced, which affect the quality of the received signals. In addition, under the same received optical power at the photodetectors, the optical modulation depth can be increased by reducing the power difference between the optical modulation sidebands and the optical carrier, which is commonly quantified by the sideband-to-carrier ratio (SCR). Currently, the optical filtering scheme is applied to achieve a better SCR value by suppressing the power of the optical carrier while maintaining that of the optical modulation sidebands. This, however, considerably reduces the overall power of the optical signal and therefore requires extra optical power amplifiers to compensate for the power loss.